Microphone transmitter for gramophones



P. E. DAVENPORT MICROPHONE TRANSMITTER FOR GRAMOPHONES Oct; 20, 1925- I1557,664

Filed Jan. 2, v19,24

Patented Oct. 20, 1925.

IHILIP' E. nAvEnI-onr, or LONDON, ENGLAND.

MICROPHONE TRANSMITTER FOR GRAMOPHONES.

Application filed January 2, 1924. Serial- No. 684,041,.

To all whom it may concern:

Be it known that I, PHILIr ERIC DAVEN- PORT, a subject of the King ofGreat Britain and Ireland, residing at 6 Meeting House Lane, London, S.E. 15 England, have invented new and useful Improvements in MicrophoneTransmitters for Gramophones, on which application has been made forLetters Patent in Great Britain, No. 641, filed the 8th January, 1923,of which the following 1s a specification. N

This invention relates to an improved construction of microphonetransmitter intended to be actuated through 'a stylus from a gramophonerecord and to modify in accordance with the recorded speech vibrationsthe current supplied to a telephone receiver employed as a reproducingdevice, or supplied to a wireless transmitter or the like.

According to the present invention, the vibrations produced in thestylus are transmitted directly and mechanically to the microphone. Thestylus bar operates the variable contacts through a cover of some highlyflexible material such as rubber so that external sounds do notalfectthe microphone and no energy is wasted in reproducing sounds. Variousother features of the invention will be apparent from the description ofthe accompanying drawings, in

.Figure 1 shows a front view of an embodiment of the invention withcertain features removed.

Figure 2 shows a side sectional view of Figure 1 adapted for use in anordinary gramophone having a tone arm.

"Figure 3 shows an outside View of Figure 1 adapted for use in apparatusonly intended to be employed as a microphone transmitter, a portion ofthe cover plate being broken away to show one of the terminal screws.

a case 1 which may be of metal, between a front plate 2 and a back plate3. These plates are of ebonite or other insulating material and buttagainst shoulders in the case .1. They are held in position by screws 4;and

nuts 5. The screws 4 are threaded through holes tapped in an inner plate6 of insulating material on which the microphone proper is built up. Apair of half ring carbon electrodes 7 are secured to the plate by cementor other suitable means, a space 8 being left between them, which may befilled with insulating material. Alternatively four quarter ringelectrodes might be used. The inner circumferences of the electrodes 7are bevelled and the space between them filled with finely dividedcarbon preferably in the form of shot. The electrodes are covered by aflexible cover 9 of insulating materialbearing on the shot. This is ofhighly flexible material such as rubber so that external sounds do notaffect it and no sounds are mechanically reproduced when the instrumentis in use. The cover 9 is held in place by nuts 10 on the screws 4. Astylus bar 11 having a cross-piece 12 threading into studs 13 secured inthe case 1 is fastened by nuts 14, rubber washers 15 being interposed toallow the stylus bar to vibrate. It will be readily understood that thestylus bar may be mounted in any other well known manner in use forgramophone reproducers. The longerend 16 of the stylus bears on thecover 9 and may be secured thereto by cement or by means of a screw orthe like. The short end of the stylus bar forms a socket in which thestylus is secured by a screw 17. A spring 18 is secured convenientlybetween nuts on one of the screws 4 so that it bears on the end 16 ofthe stylus bar and therefore in the cover 9 and the carbon shot in themicrophone. The prcssure of the spring can be varied by turning a screw19 in the front plate 2, so that the average pressure and therefore meanresistance of the microphone can beadjusted,even whenit isin use. Thecarbon electrodes are each provided with a contact screw 20 so thatconnection may be made. These screws may either project forwardlythrough the cover 9 as shown in which case the connections are madeinternally and the conductors led out at any suitable point, or they mayproject backwardly through the back plate 3, the connections being madeoutside the case. The microphone transmitter is enclosed in In the formshown in Figure 2 a spigot 21. is secured to the back plate2 so that itmay be employed in an ordinary gramophone, by removing the sound box andreplacing it with the microphone transmitter.

\Vhere apparatus solely for use therewith is employed a convenientconstruction for supporting the transmitter is shown in Figure 3. Here ahorizontal tubular arm 22 is secured to the side of the case 1 and formsa convenient channel through. which the conductors pass. The arm 22 issecured in such a position that the stylus bar 11 is at a suitable angleto the surface of the record. The

arm 22 is hinged at 23 to a vertical pivot rod 24 working in a tubularstandard 25 secured to the framework of the apparatus.

Any form of stylus, according to the type of record, may be used. Forordinary gramophone records in which the vibrations are produced bylateral displacement, ordinary steel or other needles are used. WVithrecords in which the vibrations are produced by vertical displacement, abent wire carrying a sapphire or othersuitable stylus is used, thetransmitter being carried so that the intersection of the plane of thecover with the plane of the record is perpendicular to the recordgroove.

What I claim is: Y 1. A microphone transmitter adapted t be operated bygramophone and like records comprising a casing, a microphone mountedtherein, a cover of soft fibrous material stretched across the front ofsaid microphone adapted to prevent external sounds from affecting themicrophone and means mounted on said casing for mechanicallytransmitting the vibration of the stylus to said cover.

2. A microphone transmitter adapted to be operated by gramophone andlike records comprising a casing, amicrophone mounted therein, a. coverof soft fibrous material stretched across and forming the front of saidmicrophone adapted to prevent external sounds from affecting themicrophone and a stylus bar pivoted on said casing having its end inoperative connection with the micro hone.

3. microphone transmitter adapted to be operated by gramophone and likerecords comprising a casing, a microphone susceptible only to mechanicalvibrations mounted therein, a stylus bar pivoted on said casing havingits end inoperative connection with the microphone, and an adjustablespring mounted in said casing so as to bear on said stylus bar. a O I 4.A microphone transmitter adapted to be operated by gramophone and likerecords comprising a casing,'a microphone mounted therein, a flexiblecover forming the front of said microphone adapted to prevent externalsounds from affecting the microphone, a stylus bar pivoted on saidcasing having its end in operative connection with the microphone and anadjustable sprin mountgd in said casing so as to bear on said stylus 5.A microphone transmitter adapted to be operated by gramophone andlikerecords comprising a casing, an insulated backing mounted therein, aplurality of carbon electrodes insulated from one another mounted inring formation on said backing, finely divided carbon in the spaceformed by said electrodes, a flexible insulatlng cover on saidelectrodes, means mounted on said casing for mechanically transmittingthe vibrations of the stylus to said cover and means for adjusting thenormal pressure on said cover.

mounted therein, a plurality of carbon electrodes insulated from oneanother mounted in ring formation on said backing, finely divided carbonin the space formed by said electrodes, a flexible insulating cover onsaid electrodes, a stylus bar pivoted on said casing having its end inoperative connection with said cover and an adjustable spring bearing onsaid stylus bar.

7. A microphone transmitter adapted to be operated by gramophone andlike records comprising a casing, an insulated backin mounted therein, apair of half ring shape electrodes insulated from one another mounted insaid backing, carbon shot between said electrodes, terminal screws onsaid electrodes, a flexible insulating cover secured over saidelectrodes, a stylus bar pivoted to said casing having its end inoperative connection wlth said cover, a front cover secured to saidcasin a spring mounted on said front cover an bearing on said stylus barand a screw in said front cover for adjusting the pressure of, saidspring.

8. A microphone transmitter adapted to be operated by gramophone andlike records comprising a casing, an insulated backing mounted therein,a pair of half ring sha ed electrodes insulated from one anot er mountedon said backing, carbon shot between said electrodes, terminal screws onsaid electrodes, a flexible insulating cover secured over saidelectrodes, a pair of screws in the lower end of said casing, resilientwashers on said screws, a cross-bar mounted on said screws clampedbetween said washers, a stylus bar secured to said cross-bar having itsinner end in operative connection with said cover, a socket and screw atthe outer end of said stylus bar, a front cover in said casing, a springconnected on said cover and bearing on the inner part of said stylusbar, a screw in said cover for adjusting the pressure of said spring,and means on said casing for mounting the transmitter in operativeposition.

In testimony whereof I have signed my name to this specification.

PHILIP E.v DAVENPORT.

